Method and apparatus for detecting marks on a paper web, using alternate set point values indicative of light intensity to identify marks and non-marks

ABSTRACT

Method for detecting marks (3) present on a paper web (1), which consists of successively producing and preferably recording light-intensity data in the form of intensity indications, using two alternate set-point values of light intensity representative of the presence of a mark or a non-mark. The method uses a process, deciding whether a certain light-intensity indication (V(new)j), shall be attributed to a mark, by selecting as a set-point value (V(old)j), one of the two alternate set points, either the nearest preceding indication (V(old)j) which has been adjudged as indicative of a non-mark and which essentially indicates light background of the paper web (1), or a preceding indication (V(old)j) which has been adjudged as indicative of a non-mark and which has been subjected to an intensity reduction of pre-determined magnitude (UP). There is also an apparatus for carrying out the method.

The present invention relates to a method for detecting marks or likeindications on a paper web, such as marks that have been appliedmanually to a coupon, and including the steps of transmitting images ofthe paper web to optoelectronic conversion elements located in adetecting plane or the like and operative to produce video signals whichcorresponds to the intensity of the light detected by a respectiveconversion element and emanating from an area of the paper web scannedby said element; scanning the paper web successively while successivelyproducing and preferably recording light-intensity data; attributinglight-intensity data either to the presence of a mark or to a non-markor the like on the basis of comparison with pre-determinedlight-intensity values; and compiling the thus classifiedlight-intensity data into a comprehensive image of marks present on thepaper web.

The invention also relates to apparatus for carrying out the method.

BACKGROUND OF THE INVENTION

Such methods are used, for instance, for checking betting forms, e.g.pools coupons, for the purpose of reading marks entered manually on thecoupons and for the purpose of reading information printed on saidcoupons in the form of mark locations, coupon identifying data, and likeinformation. Such coupons are normally produced from low-quality paper.

It is highly imperative that such coupons can be read reliably, notleast in the case of betting forms. It is also desirable to utilize highdetection or sensing sensitivity.

However, many factors influence the detection result and createproblems, inter alia in the interpretation of the measurements valuesobtained. For example, among other things the short beam path willresult in uneven imaging, i.e. when reading a smooth, white document theoutput signal corresponding to lamp intensity will vary considerably atdifferent parts of the arrays or rows of elements present. Thisirregularity is caused by several factors, of which the following arementioned by way of example: Different elements in the rows will havedifferent sensitivity to light; lamp defects caused by powderdistribution within the lamp will also influence the result; the shortbeam path and problems associated with wide-angle lenses of scanningoptics are also contributory factors. Furthermore, the colourdistribution and luminensce of a lamp will change with temperature andage. Further variations occur with variations resulting from theinfluence of temperature on electronic components, primarily on the rowsof conversion elements. Variations will also occur in dependence on theconstructional tolerances of the analogue components present. It must bepossible to detect marks reliably and effectively, in spite of all thecomponent-based variations that may occur.

As with all detection systems of the kind referred to here, there isfound a point at which an increase in sensitivity will result inerroneous detection, due to noise occurring in the signals and in thesystem as a whole. One example of such problem-creating phenomena ismanifested in the fact that the whiteness of the paper, the gray scale,is uneven with each individual coupon and varies from coupon to coupon,and that the marks are not totally black, but that the gray scale of themarks will vary within each individual mark and also possibly betweendifferent marks. The present system is particularly intended fordetecting hand-made or printed marks on standard white paper, and wherenoise in the measuring signals is caused, inter alia, by the aforesaidvariations.

It is known in the prior art that the presence of a mark can beestablished by applying a light-intensity set-point value, such thatlight-intensity below a given level will indicate the presence of amark. This method places great limitations on suitable sensitivities andhas a poor reliability. Some improvement can be made, by using set-pointvalues which constitute the mean values of measurement values obtainedfrom earlier measuring points.

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus which enablemarks to be detected with a high degree of reliability, whileautomatically taking into account variations resulting from paperquality, light sources, the presence of marks, etc.

Accordingly, the present invention relates to an improvement in a methodfor detecting marks which are present on a paper web, such as markswhich have been applied manually to betting coupons, including the stepsof transmitting an image of the paper web to optoelectronic conversionelements located in a detecting plane and producing video signals whichcorrespond to the intensity of the light, detected by respectiveconversion elements, emanating from an area of the paper web scanned bythe elements; scanning the paper web successively while successivelyproducing, and preferably recording, light-intensity data in the form ofintensity indications; attributing light-intensity data either to thepresence of a mark or to a non-mark on the basis of a comparison madewith pre-determined light-intensity, set-point values; attributing amark to the light-intensity indication when said indication is smallerthan the prevailing set-point value by more than a pre-determinedextent; and compiling from the thus classified light-intensity data acomprehensive image of marks present on the paper web, the improvedmethod including the aspects that when deciding whether a certainlight-intensity indication shall be attributed to a mark there is usedone of two kinds of indications as a set-point value (V(old)j), thefirst kind being the nearest preceding indication (V(old)j), in case theindication has been adjudged as indicative of a non-mark and essentiallyindicates light background of the paper web (1), and the second kindbeing a preceding indication (V(old)j), which has been adjudged asindicative of a non-mark and has been subjected to an intensityreduction of pre-determined magnitude (UP), respectively.

The invention also relates to apparatus for detecting marks present on apaper web, for example marks applied manually to a betting coupon,including components for transferring an image of the paper web tooptoelectronic conversion elements located in a detecting plane andoperative to produce video signals which corresponds to the intensity ofthe light detected by a respective conversion element and emanating froman area of the paper web as it is scanned by each of the respectiveelements, so that scanning of the paper web is carried out successivelyby successively producing and desirably recording light-intensity datain the form of light-intensity indications, and further includingapparatus for comparing the light-intensity indications withpredetermined intensity values, which are set-point values, andcomponents for attributing light-intensity data either to a mark or to anon-mark or the like on the basis of the comparison, and includingdevices operative to attribute a mark to the light-intensity indication(V(new)j) when said indication falls below a prevailing set-point value(V(old)j) by a pre-determined extent (MK); and devices for compiling thethus classified light-intensity data such as to form a comprehensiveimage of the subjects of the scan, such devices including means forselecting intensity-data set-point values (V(old)j) such that whendeciding whether a certain light-intensity indication (V(new)j) shall beattributed as indicative of a mark or a non-mark there is used one oftwo kinds of indications as a set-point value, the first being thenearest preceding indication, in case the indication has been adjudgedas indicative of a non-mark and, essentially concerns background lighton the paper web (1), and the second being a preceding indication, whichhas been adjudged as indicative of a non-mark and has been subjected tointensity decrease (UP) of a pre-determined magnitude, respectively.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail with reference to anexemplifying embodiment thereof and also with reference to theaccompanying drawings, in which

FIG. 1 is a schematic perspective view showing the principleconstruction of one embodiment of the invention;

FIGS. 2A and 2B, viewed together and referred to as FIG. 2 is a blockschematic of an inventive system;

FIG. 3 illustrates schematically the performance of the mark detectionprocess for one element of an inventive system, and shows by way ofexample the passage of a coupon which has hand-made marks, and OCR-printand a dirt stain thereon;

FIG. 4 illustrates schematically a decision matrix for the selection ofset-point values;

FIG. 5 illustrates schematically a mark and a disturbance factor in theform of a dirt stain, and also shows an imaginary or contemplatedreading window, a square filter arrangement; and

FIGS. 6a and 6b illustrate two element arrangements corresponding to a)a square filter and b) a linear filter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a paper web 1 which in the illustrated embodiment hasthe form of a pools coupon or like document, comprising a printedpattern of squares 2 forming a field 2 in which marks 3 are enteredmanually, said coupon and the marks entered thereon being readmechanically. The paper web 1 is fed through a detecting station 4, withthe aid of suitable feed device (not shown), as illustrated in FIG. 1.

The paper web 1 is illuminated in the detecting station 4, by means ofat least one lamp 5 of the fluorescent kind provided with a specialmixture of daylight red and blue powder. A lens or lens system 6 isoperative to focus an image of the paper web onto optoelectronic devices8, such as an optic array 8, positioned in a detection plane 7 or thelike. If desirable for reasons of space for example, the beam path canbe deflected with the use of one or more mirrors, not shown. Colourfilters are used to separate information detected by the optoelectronicdevices 8. The devices 8 are receptive, responsive to both red and bluelight. However, when using a blue filter, red and black marks willappear dark, whereas when using a red filter, blue, green and blackmarks will show dark.

According to one embodiment, the array of optoelectronic devices 8consist of a so-called photoarray 8 which includes 1024 elements. Moregenerally, the array 8, or devices 8, is/are intended to scan oneinformation line at a time, therewith enabling an image to be compiledas the paper web, i.e. the coupon, passes through the detecting station4. The thus compiled image is interpreted by the software of saiddevices.

The array 8 is thus intended to detect a focused image of the coupon orlike document and is constructed to convert an optical signal into twoelectric signals VIDEO A, VIDEO B, (FIG. 2A) which represent the lightintensity and which are produced in the form of a data flow, where eachelement is represented by an analogue voltage. The value of the signalis thus corresponded by the intensity of the reflected light from thescanned coupon or document falling on respective parts of the array. Thesignals VIDEO A, VIDEO B are amplified separately and freed from anyd.c. components in two separate amplifying and holding circuits 9.Signals which are thus amplified and freed from every d.c. component areconverted with the aid of separate analogue/digital converters 10, ADC10, suitably of the high-speed converter type.

The digital output signal from each ADC is given a multiplex form, andcomprises a six-bit digitalized data current corresponding to themeasured light intensity of the focused image on said array.

The digitalized data-current, here produced by a unit ARC 11 designatedan array card 11, is transmitted to a unit called an array-control card13, ACC 13 (FIG. 2B), for instance via a 34-path connector 12. Theconnector 12 is restricted in size and all signal lines have dualfunctions. Thus, a six-bit bus B1 which normally carries the digitalizedimage information will also function to transmit the values on bus B2 toa digital/analogue converter 14, DAC 14, of an amplification control 15included in the system. The digitalized data current is transferred to asynthesisor 16 and to a logic unit 19, for mark detection andfiltration, among other things.

In the case of the embodiment illustrated in FIG. 2B, the logic unit 19is incorporated in a RAM-type memory unit 18 and a PROM-type memory unit17 which are intended for use in conjunction with a mark detectionfunction 17' and a filtering function 17".

Thus, the intensity indications generated during a mark detectingprocess, such indications including the aforesaid digitalized data floware intended for comparison with pre-determined intensity values, theset-point values, and on the basis of said comparison light-intensitydata is either attributed to the presence of a mark or to a non-mark.

The logic unit 17 is programmed to select light-intensity set-pointvalues, whereby when deciding whether a certain light-intensityindication shall be attributed to the presence of a mark or a non-mark,there is used as a set-point value either the nearest precedingindication which has been judged as indicative of a non-mark and which,in the main, concerns light background of the paper web, or a precedingindication which has been judged as indicative of a non-mark and whichhas been subjected to a reduction in intensity of pre-determinedmagnitude.

The logic unit 17 is also programmed to attribute the intensityindication to a mark if said indication falls beneath the relevantset-point value by a pre-determined amount.

The logic unit 19 is also programmed so that when a selected,pre-determined reduction in light intensity is detected, the set-pointvalue will be locked to the value on the basis of which said intensityreduction was established, and is retained as the set-point or controlvalue until there is detected an intensity indication which correspondsto an intensity reduction which is smaller than said selected,pre-determined intensity reduction.

The aforesaid comparison are effected in the PROM-unit 17 in accordancewith the following simple relationship.

    ______________________________________                                        Comparison test                                                                            true              false                                          ______________________________________                                        Relationship 1:                                                                            V(OLD)j: = V(new)j                                                                              V(old)j                                        V(new)j >    (updating)        unchanged                                      (100-UP)%*V(old) j                                                            Relationship 2:                                                                            mark              non-mark                                       V(new)j <                                                                     (100-MK)%*V(old)j                                                             Relationship 3:                                                                            mark              non-mark                                       V(new)j < ABS                                                                 ______________________________________                                    

where

V(new)j=the relevant intensity indication for one element j of saidarray 8 or the like.

V(old)j=the value corresponding to element j and read from table (RAM).

UP=the limit value at which locking of a set-point value takes placeinstead of updating.

MK=the limit value at which a mark is attributed to the intensityindication concerned.

ABS=the absolute limit value for attributing a light-intensityindication of the presence of a mark.

The action of an element during passage of a coupon 1 is thus shownschematically in FIG. 3.

The path along which the coupons are intended to move is, in itself,darkened and hence the light-intensity indications which arrive at theRAM-unit when no coupon, paper web, is located in the detecting station4 will be considered to denote marks, and the set-point valuesapplicable in this case are normally the latest non-mark intendedlight-intensity indications obtained from the immediately precedingcoupon. It is not necessary to update the set-point values, andrelationships 2 and 3 will apply in this case.

The RAM-unit 18 can be set to zero, by generating a flow of incomingintensity data set to zero, and feeding this data flow to the RAM-unit.The flow of incoming data is thus zero, as is also the correspondingspace in the RAM-unit 18.

Shown at A to the left of FIG. 3 is the zero intensity corresponding tothe aforesaid zero-flow, where the presence of a mark is recorded and noupdating takes place.

Upon the termination of the zero-setting sequence, the light-intensitydata incoming at B again indicates the dark background, whereupon therelationships 1 and 3 above apply, i.e. the set-point value is updatedcontinuously and the presence of marks are recorded.

When the coupon 1, or paper web 1, reaches the detecting station, newand higher intensity indications are delivered to the RAM-unit at C,wherewith when the coupon or paper web consists of standard white paper,only the relationship 1 will apply. Non-marks are recorded.

When a mark or the like first appears on the coupon or paper web, it ispossible that the detected reduction in light-intensity will suffice tostop updating of the set-point values, i.e. to lock the set-point value,as illustrated at position D in FIG. 3, but will not suffice toattribute the mark alternative to the intensity indication. Theintensity reduction is thus greater than UP, but smaller than MK.

Since the value applicable when locking the set-point value wasnominally white, the comparison made with subsequent intensityindications concerning said mark or the like will cause the intensityindications to be attributed to the presence of a mark, since therelationship 2 is fulfilled and the relationship 3 is also fulfilled.The set-point value locked at the beginning of the mark is applicableuntil the mark ceases to be present, has passed, and, at F, the paperweb is again detected as being nominally white.

FIG. 3 also illustrates the performance of the same element whendetecting a distinct, very dark mark, such as a black OCR digit. Therelationship 2 applies in this case, and the locked set-point value isthe intensity indication at G. When this mark ceases to be present,detection returns at H to conditions according to the fulfilledrelationship 1, wherewith a nominally white coupon is detected duringcontinuous updating of the set-point values.

FIG. 3 also illustrates the manner in which a slowly changing intensitylevel corresponding to white is detected by the lens 6 as a blurredprint, with the beginning at K. The relationship 1 applies under theseconditions, and a slowly-decreasing intensity level corresponding towhite will be transmitted to the RAM-unit. This is not characteristic ofOCR-print, but can occur when the lens is incorrectly focused or in theevent of optical disturbances resulting, for instance, from dirtymirrors etc. The relationship 1 will apply during continuing updatingand no marks will be detected.

At the end of the coupon, the intensity level is maintained at Lcorresponding to white with respect to the last paper part in theRAM-unit when the flow of intensity indications return at M to indicatethe black background included by the path along which the coupons 1 orlike documents are intended to be advanced.

FIG. 6 illustrates both filter configurations, wherein F1 identifies asquare arrangement of elements 1-9, of which the element 5 is theelement under observation, and the reference F2 identifies a lineararrangement of elements 1-9, of which the element 5 is the element underobservation. Filters of this kind represent a method of reducing thequantity of information in the reproduction or image obtained by thedetecting process, or for cleansing said image. In the square filter F1the observed element 5 is modified in accordance with the eightsurrounding elements. In the case of the linear filter, modification iseffected with respect to the four elements located upstream of and thefour elements located downstream of one and the same sweep, the elementsof the linear filter being disposed sequentially in the sweep direction,perpendicular to the plane of the paper.

Filter logic 17" is preferably included in the same PROM-unit 17 as thelogic 17' for set-point selection, although the logic used in respectivefilters is separated in time. Both the linear and the square filter areused, by applying the logic state of the element concerning theaddress-input of the PROM-unit.

The performance of the filters can be programmed at different levels,and the truth tables of the filters are burned into the PROM-unit withthe coefficients used in the logic for selection of set-point values.

FIG. 5 is intended primarily to illustrate the use of filters. With theembodiment illustrated in FIG. 5, it is possible to distinguish lightintensity indications deriving from a dirt-spot, or blemish 20 on thepaper web from the light-intensity indications relating to a mark 21,while taking into account the surrounding elements.

The modus operandi of the system according to the invention, and alsothe method according to the invention, will be apparent from theaforegoing.

Thus, the coupon 1 or corresponding paper web 1 is scanned, wherewith aseries of light-intensity indications is obtained for each element inthe array 8. These light-intensity indications are processed on thebasis of the aforesaid relationships, so as to enable indications whichrelate to marks to be detected and recorded.

Register data based on scanned light-intensity indications is thenentered into the RAM-memory unit. The data entering the memory unit 18is compared continuously in the logic unit 11 with newly inserted dataand previously registered data, in the aforedescribed manner, therewithclassifying data into marks and non-marks and processing with the aid ofan appropriate filter function, whereafter the resultant informationrelating to the marks present on the paper web is sent to a centralcontrol unit, in which the information is further processed so as tocompile the desired comprehensive image of the coupon or the like. Thefollowing values have been used in the decision matrix illustrated inFIG. 4 with regard to set-point values, the attribution ofmarks/non-marks etc.:

ABS=max 10 in light intensity

UP=12%

MK=25%.

The matrix includes combinations of set-point values, real values andcorresponding "regions" of the matrix, these combinations beingreferenced 0, 1, 2 and 3. The prevailing set-point value constitutesbasic information when using the matrix, when the set-point valueV(Old)j is the value with which each new light-intensity indicationV(New)j is compared. For a given set-point value, such as 30, a "1"applies when the relationship 1 is true whereas neither relationship 2nor the relationship 3 is true, i.e. the real value is greater than orequal to the set-point value or somewhat smaller than the set-pointvalue, although not UP % or more less. The decision etc. taken inrespect of a given set-point value with successively decreasing realvalues can thus be read horizontally from the matrix. For the sameset-point value, such as 30, a "0" corresponds to the fact that therelationship 1 is false at the same time as the relationships 2 and 3are also false. Updating of the set-point values ceases herewith, but nomark is registered. A "2" indicates that the real value is MK % or moreless than the set-point value, the relationship 1 being false, therelationship 2 being true and the relationship 3 being false. As will beseen from the matrix shown in FIG. 4, in the case of the set-point value30 a "1" applies for real values down to, and including, 27; a "0"applies for real values from and including 26 down to and including 23,and a "2" applies to real values from and including 22 and downwards. A"3" is allocated to combinations of set-point values and real values forwhich the relationship 1 and the relationship 3 apply.

It will be understood from the aforegoing that the method and apparatusaccording to the present invention afford splendid possibilities ofeliminating the disturbing influence of components, such as age,deficiencies in the lens system, variation in the sensitivity ofdifferent parts of the array, etc. Thus, it is preferred that theelements of the optoelectronic devices 8 are each utilized per se, suchthat a given element is used to produce successive light-intensityindications corresponding to the light-intensity of regions lying in thedirection of movement of the paper web. This eliminates substantiallythe effect of variations in the properties of the elements therebetween.Another important advantage afforded by the invention is that prevailingsensitivity in the form of the fixed relationships UP, MK and ABSrenders the system independent of the absolute light-intensity andherewith of the paper.

It will be understood that the illustrated apparatus for carrying outthe method according to the invention can be modified in severalaspects. It is important, however, that colour filters (not shown) areplaced in the close proximity of the document. When such colour filtersare placed between the lamps 5 and the lens system 6, the filters willbe located as close as possible to the lamps 5.

In the aforegoing, an exemplifying embodiment of the invention has beendescribed with reference to the drawings. It will be understood,however, that other embodiments and minor modifications are conceivable,without departing from the concept of the invention.

For instance, the invention is not restricted for use in connectionsolely with betting coupons, such as pools coupons, but can also beapplied, for instance, with bank notes and the like for identification,checking and like purposes.

Furthermore, other, essentially known methods can be used for producinga data flow suitable for identification of marks or the like.

I claim:
 1. A method for detecting marks present on a paper web,comprising: the steps of transmitting an image of a paper web to anarray of optoelectronic conversion elements located in a detecting planeand operative to produce video signals which correspond to the intensityof reflected light detected by respective conversion elements andemanating from an area of the paper web scanned by said element; saidweb and said elements being moved relative to each other duringscanning; scanning areas of the paper web successively whilesuccessively producing light-intensity data in the form of intensityindications (Vj); attributing light-intensity data indications to thepresence of one of a mark or a non-mark on the basis of a comparisonmade with pre-determined light-intensity values, set-point values;attributing a mark to the light-intensity indication when saidindication is smaller than the prevailing pre-determined set-point valueby more than a pre-determined extent; and compiling from the thusclassified light-intensity data a comprehensive image of marks presenton the paper web, and when deciding whether a certain light-intensityindication shall be attributed to a mark using one of two kinds ofproduced light-intensity indications as a set-point value (V(old)j), thefirst being the nearest preceding light-intensity indication (V(old)j),in case the indication has been adjudged as indicative of a non-mark andessentially indicates light background of the paper web (1), and thesecond being a preceding indication (V(old)j), which has been adjudgedas indicative of a non-mark and has been subjected to an intensityreduction of pre-determined magnitude (UP), respectively.
 2. A methodaccording to claim 1, wherein said elements are each used so that agiven element produces successive light-intensity indications (Vj)corresponding to the light-intensity of regions lying in rows in thedirection of movement of the paper web (1).
 3. A method according toclaim 1, wherein said sensed and produced light-intensity indications(Vj) are placed in direct relationship with prevailing set-point values,and in that increases and decreases in light-intensity indications arenormalized on the basis of prevailing set-point values and given in, forinstance, percent (%) of prevailing set-point values.
 4. A methodaccording to claim 1, wherein, upon detection of an intensity decreaseof selected, pre-determined size (UP), the set-point value is locked tothe value (Vj) on the basis of which said intensity decrease has beenestablished, and is maintained at this value until an intensityindication is detected which corresponds to an intensity decrease whichis smaller than said selected, pre-determined intensity decrease (UP).5. A method according to claim 1, wherein said sensed and producedintensity indications (V(new)j) which lie beneath a givenpre-determined, absolute level (ABS) are always attributed as indicatinga mark.
 6. A method according to claim 1, wherein processing of anintensity indication includes the steps of processing said intensityindication with the aid of one or more filters (F1,F2), comparing theindication with pre-determined peripheral indications, and carrying outan optional probability check.
 7. Apparatus for detecting marks presenton a paper web, comprising: means for transferring an image of the paperweb to and including an array of optoelectronic conversion elementslocated in a detecting plane or the like and operative to produce videosignals which correspond to the intensity of the light detected by arespective conversion element and emanating from an area of the paperweb scanned by each said element of said array, including means forrelatively moving said web and the detecting plane, whereby scanning ofthe paper web is carried out successively while successively producinglight-intensity data in the form of light-intensity indications, andcomprising further means for comparing said light-intensity indicationswith pre-determined light-intensity values, set-point values, and meansfor attributing light-intensity data to one of a mark or a non-mark onthe basis of the comparison, and means (17') operative to attribute amark to the scanned and produced light-intensity indication (V(new)j)when said indication falls below a prevailing set-point value (V(old)j)by a pre-determined extent (MK); and means for compiling the thusclassified light-intensity data such as to form a comprehensive image ofthe subjects of the scan, and further including means (19) for selectingintensity-data set-point values (V(old)j) such that when decidingwhether a certain scanned and produced light-intensity indication(V(new)j) shall be attributed as indicative of one of a mark and anon-mark, there is used one of two kinds of indications as a set-pointvalue, a first set-point being the nearest preceding light-intensityindication, in case the indication was adjudged as indicative of anon-mark and, essentially concerns background light on the paper web(1), and a second set-point being a preceding indication, which has beenadjudged as indicative of a non-mark and has been subjected to intensitydecrease (UP) of pre-determined magnitude, respectively.
 8. Apparatusaccording to claim 7, wherein each individual element of said array isoperative to produce successive light-intensity indications (Vj)corresponding to the light-intensity of regions lying in a row in themovement direction of the paper web (1).
 9. Apparatus according to claim7, wherein set-point value selecting means (19) are provided and placelight-intensity indications in direct relationship with prevailingset-point values, so that increases and decreases are intended to benormalized on the basis of prevailing set-point values and are given inpercent (%) of the prevailing set-point value.
 10. Apparatus accordingto claim 7, including means which detect an intensity decrease ofselected, pre-determined value (UP) and render the set-point valueselecting means (19) operative to lock the set-point value to the valueon the basis of which said intensity decrease was established, and tomaintain said locked in set-point value until there is detected alight-intensity indication which corresponds to a light-intensitydecrease which is smaller than said previously selected, pre-determinedlight-intensity decrease (UP).
 11. Apparatus according to claim 7,wherein said set-point value selecting means (19) includes means whichprovide that light-intensity indications which lie beneath a givenpredetermined, absolute level (ABS) are always attributed to a mark. 12.Apparatus according to claim 7, wherein one or more light filters (F1,F2) are provided and placed between the array of optoelectronicconversion elements and the light which is being sensed by said elementsto provide a desired intensity indication, said desired intensityindication being intended for comparison with pre-determined, peripheralindications and a probability check being carried out.
 13. A method asdefined in claim 1, including the further step of recording thesuccessively produced light-intensity data.
 14. Apparatus as defined inclaim 7, further including means in said first named means whichsuccessively produces light-intensity data to enable recording of saidproduced light-intensity data.